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Leprechauns, satyrs, peasants, elementals, trolls, mummies, troglodytes – can be very useful at the beginning of the game or in a rapidly developing war where you don't have to make choices. Leprechauns are useful because of their luck, and luck sometimes helps to win. A satyr with the "enthusiasm" spell can also be very useful, and higher morale sometimes plays an exceptional role and becomes the key to victory. A peasant brings gold; if you are short by 1 unit of gold and cannot hire an angel, you lose. If you had a peasant, its benefit of 1 unit of gold per day could allow you to hire an angel and win. Trolls are very useful with their regeneration, and creatures of the same level as a troll (level 2) find it difficult to defeat it. Mummies cast a curse on enemy creatures or a hero. Under the influence of the curse, the characteristics of creatures are reduced. A troglodyte can distract the enemy from the hero or serve as cannon fodder.
All of this shows that every creature has some benefit; you just need to see and understand it. And in certain situations, even the strongest creature can be useless compared to a satyr.